Catheters with control modes for interchangeable probes

ABSTRACT

A medical system including a catheter containing a mechanical system that is remotely operable uses a sensor to at least partly measure a pose of the catheter and a control system coupled to the mechanical system. The control system has multiple operating modes including one or more holding modes in which the control system operates the mechanical system to maintain a working configuration of the catheter based on feedback from the sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent document is related to and incorporates by reference thefollowing co-filed patent applications: U.S. Pat. App. No. Unknown,Attorney Docket No. ISRG03170/US, entitled “Catheters with Control Modesfor Interchangeable Probes”; U.S. Pat. App. No. Unknown, Attorney DocketNo. ISRG03230/US, entitled “Vision Probe and Catheter Systems”; and U.S.Pat. App. No. Unknown, Attorney Docket No. ISRG03590/US, entitled“Catheter Sensor Systems.”

BACKGROUND

Medical devices that navigate body lumens need to be physically smallenough to fit within the lumen. Lung catheters, for example, which maybe used to perform minimally invasive lung biopsies or other medicalprocedures, may need to follow airways that decrease in size as thecatheter navigates branching passages. To reach a target location in alung, a catheter may need to follow passages having diameters as smallas 3 mm or less. Manufacturing a catheter that includes the mechanicalstructures suitable for remote or robotic operation and that has adiameter that is sufficiently small to navigate such small lumens can bechallenging. In particular, one desirable configuration for remotelyoperated catheter would provide a tool mounted on a flexible distal tip;tendons or pull wires that extend down the length of the catheter to anexternal drive system that pulls on the tendons to actuate the tool ordistal tip; lumens for suction and/or irrigation; a vision system forviewing of the target location; and sensors to identify the location ofthe instrument relative to a patient's body. Accommodating all of thedesired features and elements of a lung catheter or other device havinga diameter about 3 mm or less can be difficult.

SUMMARY

In accordance with an aspect of the invention, a catheter control systemhas a control mode (sometimes referred to herein as a holding mode) thatactively maintains the catheter in a working configuration desired for amedical procedure. This holding mode facilitates use of the cathetersystem with interchangeable probes. In particular, a vision probe can bedeployed in the catheter while the catheter navigates to a work site, toview the work site, or to assist in identifying the desired workingconfiguration for the catheter during performance of a medical task. Thecatheter control system can then switch into the holding mode, and thevision system can be removed. A medical probe can then be deployedthrough the catheter in place of the removed vision probe, and thecontrol system maintains the working configuration and allowsperformance of a medical task without the vision probe, while thedesired working configuration is fixed and held. In one implementation,the control system actively keeps the catheter in the desired workingconfiguration while the medical probe is inserted through the catheter,reaches the work site, and performs a medical function. In analternative implementation, the control system returns the catheter tothe recorded working configuration before the medical function isperformed. Since the catheter only needs to accommodate the vision ormedical probe and not both, the diameter of the catheter may be smallerthan might otherwise be possible for a convention system that providessimilar functionality.

In accordance with another aspect of the invention, a feedback controlmethod and system for a robotically controlled flexible deviceimplements multiple different modes of closed-loop device actuation orstiffening for different applications and usage scenarios. The differentstiffening modes can cause the device to respond in a desired way incase of externally applied forces, for example, tissue reaction forcesas the device navigates through a clinical space or as the deviceinteracts with tissue as part of a medical procedure. Details concerningfeedback control methods and systems for robotically controlled flexibledevices may be found in U.S. patent application Ser. No. 12/780,417(filed May 14, 2010; disclosing “Drive Force Control in MedicalInstrument Providing Position Measurements”) and in U.S. patentapplication Ser. No. 12/945,734 (filed Nov. 12, 2010; disclosing“Tension Control in Actuation of Multijoint Medical Instrument”), bothof which are incorporated herein by reference.

In one embodiment, a flexible device such as a catheter uses real-timefeedback from a sensor system in generation of signals for actuatorsattached to tendons that are used to articulate a distal portion of thedevice. For example, a catheter may include a flexible section at itsdistal tip that can bend in two directions (pitch and yaw). Afiber-optic shape sensor can measure the bending of the flexible sectionand return measurement data indicating the position and orientation ofthe distal tip relative to a base of the shape sensed. The position ofthe base may be determined, for example, using electromagnetic sensorsthat provide measurements of a position and orientation of the baserelative to an external reference that may be attached to a patient.Multiple actuation tendons (e.g., pull wires or cables) attach to thedistal tip and run along the length of the catheter to the actuators.Control logic that controls the actuators to pull the tendons and hencemove the distal tip in any pitch/yaw direction can operate in differentmodes for different purposes. In particular, for a holding mode, thecontrol logic can use the sensor data and fixed information on a targetshape of the catheter to compute control signals for the actuators.

The control logic for a robotic catheter or other flexible system mayhave multiple modes of operation including one or more of the following:1.) A position stiffness mode in which the control system controlsactuators to minimize a difference between desired and measuredpositions of the distal tip of the catheter or probe; 2.) An orientationstiffness mode in which the control system controls the actuators tominimize a difference between desired and measured pointing directionsof the distal tip; 3.) A target position stiffness mode in which thecontrol system uses a combination of the measured tip position andpointing direction to control the distal tip to always point towards aspecified target point; and 4.) A target axial motion stiffness mode inwhich the control system uses a combination of the measured tip positionand pointing direction, together with sensor measurements from otherparts of the device, and controls actuators to ensure that the distaltip is positioned on a specific line in space and has a pointingdirection also along that line. The selection of which of the availablemodes the control system uses can be made through user selection,according to the type of probe being used (e.g. forceps, camera, laser,brush, or needle), or according to the action the catheter is performing(e.g., navigating or performing a biopsy). Any of these modes can beused to hold the catheter for a medical procedure by fixing the desiredlocation, direction, target point, or line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a robotic catheter system in accordance with an embodimentof the invention having multiple control modes.

FIG. 2 shows an embodiment of an actuated distal tip that can beemployed in the system of FIG. 1.

FIGS. 3A and 3B show cross-sectional views of proximal and distalsections of a catheter in accordance with an embodiment of theinvention.

FIG. 4 shows a cross-sectional view of a vision probe that may bedeployed in the catheter of FIGS. 3A and 3B and swapped out for use ofmedical probes in the catheter shown in FIGS. 3A and 3B.

FIG. 5 is a flow diagram of a process for using the catheter system witha removable vision system and multiple control modes.

FIG. 6 is a flow diagram of a catheter control process in a steeringmode.

Use of the same reference symbols in different figures indicates similaror identical items.

DETAILED DESCRIPTION

A catheter system can employ a vision probe that is interchangeable withone or more medical probes or tools. The vision probe can be removed andreplaced with a medical probe used in a medical procedure. Theinterchanging of the vision and medical probes may permit the cathetersystem to have a smaller diameter and thus navigate smaller passagesthan would a similar system that simultaneously accommodates both visionand medical systems. Alternatively, interchanging probes allow morespace for vision and medical systems having greater functionality thanmight a catheter that must simultaneously accommodate both vision andmedical systems.

One method for using a catheter system includes steering a catheteralong a body lumen for at least part of the path to a work site for amedical procedure. A vision system may then be deployed in the catheterduring the steering and/or used to view the work site reached whennavigation is complete. The vision system can also be used to helpidentify a desired working configuration for the catheter and whenmanipulating the catheter into the desired working configuration. Thecontrol system of the catheter can then record the working configurationand may be placed in a “holding” mode in which the pose of the catheterrelative to a patient is monitored and the catheter is actuated toactively maintain or return to the recorded working configuration. Thecontrol system may provide different types of control modes, which maybe useful for different types of medical probes or different types ofmedical procedures. For example, if the medical probe includes a laser,a combination of the location and orientation of the distal tip of thecatheter can be controlled so that the distal tip remains targeted on aspecific location in the patient. An alternative holding mode canmaintain the location of the distal tip of the catheter while permittingthe orientation of the distal tip to change or maintain a distal tipalong a line.

FIG. 1 schematically illustrates a catheter system 100 in accordancewith one embodiment of the invention. In the illustrated embodiment,catheter system 100 includes a catheter 110, a drive interface 120,control logic 140, an operator interface 150, and a sensor system 160.

Catheter 110 is a generally flexible device having one or more lumensincluding a main lumen that can accommodate interchangeable probes suchas described further below. Flexible catheters can be made using abraided structure such as a woven wire tube with inner or outer layersof a flexible or low friction material such as polytetrafluoroethylene(PTFE). In one embodiment, catheter 110 includes a bundle of lumens ortubes held together by a braided jacket and a reflowed (i.e., fused bymelting) jacket of a material such as Polyether Block Amide (Pebax). Anadditional tip section (e.g., a metal structure such as shown in FIG. 2and described further below) can be attached at the distal end ofcatheter 110. Alternatively, an extrusion of a material such as Pebaxcan similarly be used to form multiple lumens in catheter 110. Catheter110 particularly includes a main lumen for interchangeable probe systemsand smaller lumens for pull wires and sensor lines. In the illustratedembodiment, catheter 110 has a proximal section 112 attached to driveinterface 120 and a distal section 114 that extends from the proximalsection 112. Pull wires extend from drive system 120 through proximalsection 112 and distal section 114 and connect to a steerable distalsteerable segment 116.

The overall length of catheter 110 may be about 60 to 80 cm or longerwith distal section 114 being about 15 cm long and steerable segment 116being about 4 to 5 cm long. In accordance with an aspect of theinvention, distal section 114 has a smaller diameter than does proximalsection 112 and thus can navigate smaller natural lumens or passages.During a medical procedure, at least a portion of proximal section 112and all of distal section 114 may be inserted along a natural lumen suchas an airway of a patient. The smaller diameter of distal section 114permits use of distal section 114 in lumens that may be too small forproximal section 112, but the larger diameter of distal section 114facilitates inclusion of more or larger structures or devices such aselectromagnetic (EM) sensors 162 that may not fit in distal section 114.

Steerable segment 116 is remotely controllable and particularly has apitch and a yaw that can be controlled using pull wires. Steerablesegment 116 may include all or part of distal section 114 and may besimply implemented as a multi-lumen tube of flexible material such asPebax. In general, steerable segment 116 is more flexible than theremainder of catheter 110, which assists in isolating actuation orbending to steerable segment 116 when drive interface 120 pulls onactuating tendons. Catheter 110 can also employ additional features orstructures such as use of Bowden cables for actuating tendons to preventactuation from bending proximal section 112 (or bending any portion thesection of 114 other than steerable segment 116) of catheter 110. FIG. 2shows one specific embodiment in which steerable segment 116 is madefrom a tube 210 that in catheter 110 of FIG. 1 contains multiple tubesdefining a main lumen for a probe system and smaller lumens foractuation tendons 230 and a shape sensor not shown in FIG. 2. In theillustrated embodiment, tendons 230 are placed 90° apart surroundinglumen 312 to facilitate steering catheter 110 in pitch and yawdirections defined by the locations of tendons 230. A reflowed jacket,which is not shown in FIG. 2 to better illustrate the internal structureof steerable segment 116, may also cover tube 210. As shown in FIG. 2,tube 210 is cut or formed to create a series of flexures 220. Tendons230 connect to a distal tip 215 of steerable segment 116 and extend backto a drive interface 120. Tendons 230 can be wires, cables, Bowdencables, hypotubes, or any other structures that are able to transferforce from drive interface 120 to distal tip 215 and limit bending ofproximal section 112 when drive interface 120 pulls on tendons 230. Inoperation, pulling harder on any one of tendons 230 tends to causesteerable segment 116 to bend in the direction of that tendon 230. Toaccommodate repeated bending, tube 210 may be made of a material such asNitinol, which is a metal alloy that can be repeatedly bent with littleor no damage.

Drive interfaces 120 of FIG. 1, which pulls on tendons 230 to actuatedistal steerable segment 116, includes a mechanical system ortransmission 124 that converts the movement of actuators 122, e.g.,electric motors, into movements of (or tensions in) tendons 230 that runthrough catheter 110 and connect to distal steerable segment 116. (Pushrods could conceivably be used in catheter 110 instead of pull wires butmay not provide a desirable level of flexibility.) The movement and poseof distal steerable segment 116 can thus be controlled through selectionof drive signals for actuators 122 in drive interface 120. In additionto manipulating tendons 230, drive interface 120 may also be able tocontrol other movement of catheter 110 such as range of motion in aninsertion direction and rotation or roll of the proximal end of catheter110, which may also be powered through actuators 122 and transmission124. Backend mechanisms or transmissions that are known forflexible-shaft instruments could in general be used or modified fordrive interface 120. For example, some known drive systems for flexibleinstruments are described in U.S. Pat. App. Pub. No. 2010/0331820,entitled “Compliant Surgical Device,” which is hereby incorporated byreference in its entirety. Drive interface 120 in addition to actuatingcatheter 110 should allow removal and replacements of probes in catheter110, so that the drive structure should be out of the way during suchoperations.

A dock 126 in drive interface 120 can provide a mechanical couplingbetween drive interface 120 and catheter 110 and link actuation tendonsto transmission 124. Dock 126 may additionally contain electronics forreceiving and relaying sensor signals from portions of sensor system 160in catheter 110 and an electronic or mechanical system for identifyingthe probe or the type of probe deployed in catheter 110.

Control logic 140 controls the actuators in drive interface 120 toselectively pull on the tendons as needed to actuate and steer distalsteerable segment 116. In general, control logic 140 operates inresponse to commands from a user, e.g., a surgeon or other medicalpersonnel using operator interface 150, and in response to measurementsignals from sensor system 160. However, in holding modes as describedfurther below, control logic 140 operates in response to measurementsignals from sensor system 160 to maintain or acquire a previouslyidentified working configuration. Control logic 140 may be implementedusing a general purpose computer with suitable software, firmware,and/or interface hardware to interpret signals from operator interface150 and sensor system 160 and to generate control signals for driveinterface 120.

In the illustrated embodiment, control logic 140 includes multiplemodules 141, 142, 143, and 144 that implement different processes forcontrolling the actuation of catheter 110. In particular, modules 141,142, 143, and 144 respectively implement a position stiffening mode, anorientation stiffening mode, a target position mode, and a target axialmode, which are described further below. A module 146 selects whichcontrol process will be used and may base the selection on user input,the type or status of the probe deployed in catheter 110, and the taskbeing performed. Control logic 140 also includes memory storingparameters 148 of a working configuration of distal steerable segment116 that is desired for a task, and each of the modules 141, 142, 143,and 144 can uses their different control processes to actively maintainor hold the desired working configuration.

Operator interface 150 may include standard input/output hardware suchas a display, a keyboard, a mouse, a joystick, or other pointing deviceor similar I/O hardware that may be customized or optimized for asurgical environment. In general, operator interface 150 providesinformation to the user and receives instructions from the user. Forexample, operator interface 150 may indicate the status of system 100and provide the user with data including images and measurements made bysystem 100. One type of instruction that the user may provide throughoperator interface 150, e.g., using a joystick or similar controller,indicates the desired movement or position of distal steerable segment116, and using such input, control logic 140 can generate controlsignals for actuators in drive interface 120. Other instructions fromthe user can select an operating mode of control logic 140.

Sensor system 160 generally measures a pose of distal steerable segment116. In the illustrated embodiment, sensor system 160 includes EMsensors 162 and a shape sensor 164. EM sensors 162 include one or moreconductive coils that may be subjected to an externally generatedelectromagnetic field. Each coil of EM sensors 162 then produces aninduced electrical signal having characteristics that depend on theposition and orientation of the coil relative to the externallygenerated electromagnetic field. In an exemplary embodiment, EM sensors162 are configured and positioned to measure six degrees of freedom,e.g., three position coordinates X, Y, and Z and three orientationangles indicating pitch, yaw, and roll of a base point. The base pointin system 100 is at or near the end of proximal section 112 and thestart of distal section 114 of catheter 110. Shape sensor 164 in theexemplary embodiment of the invention includes a fiber grating thatpermits determination of the shape of a portion of catheter 110extending from the base point, e.g., the shape of distal section 114 ordistal steerable segment 116. Such shape sensors using fiber gratingsare further described in U.S. Pat. No. 7,720,322, entitled “Fiber OpticShape Sensor,” which is hereby incorporated by reference in itsentirety. An advantage of the illustrated type of sensor system 160 isthat EM sensors 162 can provide measurements relative to the externallygenerated electrical field, which can be calibrated relative to apatient's body. Thus, system 160 can use EM sensors 162 to reliablymeasure the position and orientation of a base point for shape sensor164, and shape sensor 164 need only provide shape measurement for arelatively short distance. Additionally, distal section 114 onlycontains shape sensor 164 and may have a diameter that is smaller thanthe diameter of proximal section 112. More generally, sensor system 160need only be able to measure the pose of distal steerable segment 116,and other types of sensors could be employed.

FIGS. 3A and 3B respectively show cross-sections of the proximal anddistal sections 112 and 114 of catheter 110 in one embodiment of theinvention. FIG. 3A shows an embodiment of catheter 110 having a body 310that includes a main lumen 312 for a vision or medical probe, lumens 314containing tendons 230, lumens 316 containing EM sensors 162 orassociated signal wires, and a lumen 318 containing a fiber shape sensor164. Main lumen 312, wire lumens 314, and a shape sensor lumen 318extend into distal section 114 as shown in FIG. 3B, but lumens 316 forEM sensors 162 are not needed in distal section 114 because EM sensors162 are only in proximal section 112. Accordingly, distal section 114can be smaller than proximal section 112. In an exemplary embodiment,body 310 in proximal section 112 has an outer diameter of about 4 mm(e.g., in a range from 3 to 6 mm) and provides main lumen 312 with adiameter of about 2 mm (e.g., in a range from 1 to 3 mm) and in distalsection 114 has an outer diameter of about 3 mm (e.g., in a range from 2to 4 mm) while maintaining the diameter of main lumen 312 at about 2 mm.A smooth taper (as shown in FIG. 1) or an abrupt step in body 310 can beused at the transition from the larger diameter of proximal section 112to the smaller diameter of distal section 116.

The specific dimensions described in above are primarily for a catheterthat accommodates probes having a diameter of about 2 mm, which is astandard size for existing medical tools such as lung biopsy probes.However, alternative embodiments of the invention could be made largeror smaller to accommodate medical probes with a larger or smallerdiameter, e.g., 1 mm diameter probes. A particular advantage of suchembodiments is that a high level of functionality is provided in acatheter with relative small outer diameter when compared to the size ofprobe used in the catheter.

FIGS. 3A and 3B also show a sheath 360 that may be employed betweencatheter body 310 and a probe in main lumen 312. In one embodiment ofcatheter 110, sheath 360 is movable relative to body 310 can be extendedbeyond the end of distal steerable segment 116. This may be advantageousin some medical procedures because sheath 360 is even smaller thandistal section 114 and therefore may fit into smaller natural lumens orpassages. For example, if catheter 110 reaches a branching of lumensthat are too small to accommodate distal steerable segment 116, distalsteerable segment 116 may be pointed in the direction of the desiredbranch, so that sheath 360 can be pushed beyond the end of distalsteerable segment 116 and into that branch. Sheath 360 could thusreliably guide a medical probe into the desired branch. However, sheath360 is passive in that it is not directly actuated or steerable. Incontrast, distal section 116 accommodates pull wires 230 that connect todistal steerable segment 116 and can be manipulated to steer or posedistal steerable segment 116. In some medical applications, the activecontrol of distal steerable segment 116 is desirable or necessary duringa medical procedure, and passive sheath 360 may not be used in someembodiments of the invention.

Main lumen 312 is sized to accommodate a variety of medical probes. Onespecific probe is a vision probe 400 such as illustrated in FIG. 4.Vision probe 400 has a flexible body 410 with an outer diameter (e.g.,about 2 mm) that fits within the main lumen of catheter 110 and withmultiple inner lumens that contain the structures of vision probe 400.Body 410 may be formed using an extruded flexible material such asPebax, which allows creation of multiple lumens. In the illustratedembodiment, the structure of vision probe 400 includes a CMOS camera420, which is at the distal end of the probe and connected through oneor more signal wires (not shown) that extend along the length of visionprobe 400, e.g., to provide a video signal to control logic 140 oroperator interface 150 as shown in FIG. 1. Vision probe 400 alsoincludes illumination fibers 430 that provide light for imaging within abody lumen and fluid ports 326 for suction and irrigation that may beuseful, for example, for rinsing of a lens of camera 420. Additionally,vision probe 400 may include an electromagnetic sensor (not shown)embedded just proximally to camera 420 to provide additional poseinformation about the tip of vision probe 400.

Vision probe 400 is adapted to be inserted or removed from catheter 110while catheter 110 is in use for a medical procedure. Accordingly,vision probe 400 is generally free to move relative to catheter 110.While movement relative to catheter 110 is necessary or desirable duringinsertion or removal of vision probe 400, the orientation of a visionprobe 400 (and some medical probes) may need to be known for optimal oreasier use. For example, a user viewing video from vision probe 400 andoperating a controller similar to a joystick to steer catheter 110generally expects the directions of movement of the controller tocorrespond to the response of distal steerable segment 116 and theresulting change in the image from vision probe 400. Operator interface150 needs (or at least can use) information on the orientation of visionprobe 400 relative to tendons 230 in order to provide a consistency indirections used in the user interface. In accordance with an aspect ofthe invention, a keying system (not shown) can fix vision probe 400 intoa known orientation relative to catheter 110 and tendons 230. The keyingsystem may, for example, include a spring, fixed protrusion, or latch onvision probe 400 or distal steerable segment 116 and a complementarynotch or feature in distal steerable segment 116 or vision probe 400.

Vision probe 400 is only one example of a probe system that may bedeployed in catheter 110 or guided through catheter 110 to a work site.Other probe systems that may be used include, but are not limited to,biopsy forceps, biopsy needles, biopsy brushes, ablation lasers, andradial ultrasound probes. In general, catheter 110 can be used withexisting manual medical probes that are commercially available frommedical companies such as Olympus Europa Holding GmbH.

The catheter system 100 of FIG. 1 can be used in procedures that swap avision probe and a medical probe. FIG. 5 is a flow diagram of oneembodiment of a process 500 for using the catheter system 100 of FIG. 1.In process 500, vision probe 400 is deployed in catheter 110 in step510, and catheter 110 is inserted along a path including a natural lumenof a patient. For example, for a lung biopsy, distal steerable segment116 of catheter 110 may be introduced through the mouth of a patientinto the respiratory tract of the patient. Vision probe 400 when fullydeployed in catheter 110 may fit into a keying structure that keepsvision probe 400 in a desired orientation at or even extending beyonddistal steerable segment 116 to provide a good forward view from thedistal steerable segment 116 of catheter 110. As noted above, distalsteerable segment 116 of catheter 110 is steerable, and vision probe 320can provide video of the respiratory tract that helps a user whennavigating catheter 110 toward a target work site. However, use ofvision probe 400 during navigation is not strictly necessary sincenavigation of catheter 110 may be possible using measurements of sensorsystem 160 or some other system with or without vision probe 400 beingdeployed or used in catheter 110. The path followed to the work site maybe entirely within natural lumens such as the airways of the respiratorytrack or may pierce and pass through tissue at one or more points.

When steerable segment 116 reaches the target work site, vision probe400 can be used to view the work site as in step 530 and to posesteerable segment 116 for performance of a task at the target work siteas in step 540. Posing of steerable segment 116 may use images or visualinformation from vision probe 400 and measurements from sensor system160 to characterize the work site and determine the desired workingconfiguration. The desired working configuration may also depend on thetype of tool that will be used or the next medical task. For example,reaching a desired working configuration of catheter 110 may bring thedistal tip of steerable segment 116 into contact with tissue to betreated, sampled, or removed with a medical tool that replaces visionprobe 400 in catheter 110. Another type of working configuration maypoint steerable segment 116 at target tissue to be removed using anablation laser. For example, tissue could be targeted in one or more 2Dcamera views while vision probe 400 is still in place in catheter 110,or target tissue can be located on a virtual view of the work site usingpre-operative 3D imaging data together with the position sensingrelative to patient anatomy. Still another type of working configurationmay define a line for the insertion of a needle or other medical toolinto tissue, and the working configuration includes poses in which thedistal tip of steerable segment 116 is along the target line. Ingeneral, the desired working configuration defines constraints on theposition or the orientation of the distal tip of steerable segment 116,and the shape of more proximal sections of catheter 110 is not similarlyconstrained and may vary as necessary to accommodate the patient.

Step 550 stores in memory of the control logic parameters that identifythe desired working configuration. For example, the position of a distaltip or target tissue can be defined using three coordinates. A targetline for a need can be defined using the coordinates of a point on theline and angles indicating the direction of the line from that point. Ingeneral, control logic 120 uses the stored parameters that define thedesired working configuration when operating in a holding mode thatmaintains distal steerable segment 116 of catheter 110 in the desiredworking configuration as described further below.

Step 560 selects and activates a holding mode of the catheter systemafter the desired working configuration has been established andrecorded. Control logic 140 for catheter 110 of FIG. 1 may have one ormore modules 141, 142, 143, and 144 implementing multiple stiffeningmodes that may be used as holding modes when the desired configurationof steerable segment 116 has fixed constraints. The available controlmodes may include one or more of the following.

1.) A position stiffness mode compares the position of the distal tip ofsteerable segment 116 as measured by sensor system 160 to a desired tipposition and controls the actuators to minimize the difference indesired and measured tip positions. The position stiffness mode mayparticularly be suitable for general manipulation tasks in which theuser tries to precisely control the position of the tip and forsituations where the distal tip contacts tissue.

2.) An orientation stiffness mode compares the measured orientation orpointing direction of the distal tip to a desired pointing direction ofthe distal tip and controls the actuators to minimize the difference indesired and actual tip pointing direction. This orientation stiffeningthat may be suitable, e.g., when controlling an imaging device such asvision probe 400 attached steerable segment 116, in which case theviewing direction is kept as desired, while the exact position ofsteerable segment 116 may be less important.

3.) A target position stiffness mode uses a combination of the measuredtip position and pointing direction to control catheter 110 to alwayspoint the distal tip of steerable segment 116 towards a specified targetpoint some distance in front of steerable segment 116. In case ofexternal disturbances, control logic 140 may control the actuators toimplement this target position stiffening behavior, which may besuitable, e.g., when a medical probe inserted though the cathetercontains an ablation laser that should always be aimed at a targetablation point in tissue.

4.) A target axial motion stiffness mode uses a combination of themeasured tip position and pointing direction to ensure that the distaltip of steerable segment 116 is always on a line in space and has apointing direction that is also along that line. This mode can beuseful, e.g., when inserting a biopsy needle along a specified line intotissue. Tissue reaction forces could cause the flexible section ofcatheter 110 to bend while inserting the needle, but this controlstrategy would ensure that the needle is always along the right line.

The selection of a mode in step 560 could be made through manualselection by the user, based on the type of probe that is being used(e.g., grasper, camera, laser, or needle) in catheter 110, or based onthe activity catheter 110 is performing. For example, when a laser isdeployed in catheter 110, control logic 120 may operate in positionstiffness mode when the laser deployed in catheter 110 is off andoperate in target position stiffness mode to focus the laser on adesired target when the laser is on. When “holding” is activated,control logic 140 uses the stored parameters of the workingconfiguration (instead of immediate input from operator interface 150)in generating control signals for drive interface 120.

The vision probe is removed from the catheter in step 570, which clearsthe main lumen of catheter 110 for the step 580 of inserting a medicalprobe or tool through catheter 110. For the specific step order shown inFIG. 5, control logic 140 operates in holding mode and maintains distalsteerable segment 116 in the desired working configuration while thevision system is removed (step 570) and the medical probe is inserted(step 580). Accordingly, when the medical probe is fully deployed, e.g.,reaches the end of distal steerable segment 116, the medical probe willbe in the desired working configuration, and performance of the medicaltask as in step 590 can be then performed without further need or use ofthe removed vision probe. Once the medical task is completed, thecatheter can be taken out of holding mode or otherwise relaxed so thatthe medical probe can be removed. The catheter can then be removed fromthe patient if the medical procedure is complete, or the vision oranother probe can be inserted through the catheter if further medicaltasks are desired.

In one alternative for the step order of process 500, catheter 110 maynot be in a holding mode while the medical probe is inserted but can beswitched to holding mode after the medical probe is fully deployed. Onceholding mode is initiated, control logic 140 will control the driveinterface 130 to return distal steerable segment 116 to the desiredworking configuration if distal steerable segment 116 has moved sincebeing posed in the desired working configuration. Thereafter, controllogic 140 monitors the pose of distal steerable segment 116 and activelymaintains distal steerable segment 116 in the desired workingconfiguration while the medical task is performed in step 590.

FIG. 6 shows a flow diagram of a process 600 of a holding mode that canbe implemented in control logic 140 of FIG. 1. Process 600 begins instep 610 with receipt of measurement signals from sensor system 160. Theparticular measurements required depend on the type of holding modebeing implemented, but as an example, the measurements can indicateposition coordinates, e.g., rectangular coordinates X, Y, and Z, of thedistal tip of steerable segment 116 and orientation angles, e.g., anglesθ_(X), θ_(Y), and θ_(Z) of a center axis of the distal tip of steerablesegment 116 relative to coordinate axes X, Y, and Z. Other coordinatesystems and methods for representing the pose of steerable segment 116could be used, and measurements of all coordinates and direction anglesmay not be necessary. However, in an exemplary embodiment, sensor system160 is capable of measuring six degrees of freedom (DoF) of the distaltip of steerable segment 116 and of providing those measurements tocontrol logic 140 in step 610.

Control logic 140 in step 620 determines a desired pose of distalsteerable segment 116. For example, control logic 140 can determinedesired position coordinates, e.g., X′, Y′, and Z′, of the end of distalsteerable segment 116 and desired orientation angles, e.g., anglesθ′_(X), θ′_(Y), and θ′_(Z) of the center axis of distal steerablesegment 116 relative to coordinate axes X, Y, and Z. The holding modesdescribed above generally provide fewer than six constraints on thedesired coordinates. For example, position stiffness operates toconstrain three degrees of freedom, the position of the end of distalsteerable segment 116 but not the orientation angles. In contrast,orientation stiffness mode constrains one or more orientation angles butnot the position of end of distal steerable segment 116. Target positionstiffness mode constrains four degrees of freedom, and axial stiffnessmode constrains five degrees of freedom. Control logic 610 can imposefurther constraints to select one of set of parameters, e.g., X′, Y′,and Z′ and angles θ′_(X), θ′_(Y), and θ′_(Z), that provides the desiredworking configuration. Such further constraints include but are notlimited to mechanical constraints required by the capabilities of distalsteerable segment 116 and of catheter 110 generally and utilitarianconstraints such as minimizing movement of distal steerable segment 116or providing desired operating characteristics such as smooth,non-oscillating, and predictable movement with controlled stress incatheter 110. Step 620 possibly includes just keeping a set pose distalsteerable segment 116 by finding smallest movement from the measuredpose to a pose satisfying the constraints, e.g., finding the point onthe target line closest to the measure position for axial motionstiffness or finding some suitable pose from registered pre-op data thatis close to the current pose.

Control logic 140 in step 630 uses the desired and/or measured poses todetermine corrected control signals that will cause drive interface 120to move distal steerable segment 116 to the desired pose. For example,the mechanics of catheter 110 and drive interface 120 may permitdevelopment of mappings from the desired coordinates X′, Y′, and Z′ andangles θ′_(X), θ′_(Y), and θ′_(Z) to actuator control signals thatprovide the desired pose. Other embodiments may use differences betweenthe measured and desired pose to determine corrected control signals. Ingeneral, the control signals may be used not only to control actuatorsconnected through tendons to distal steerable segment 116 but may alsocontrol (to some degree) insertion or roll of catheter 110 as a whole.

A branch step 650 completes a feedback loop by causing process 600 toreturn to measurement step 610 after control system 140 applies newcontrol signals drive interface 120. The pose of distal tip is thusactively monitored and controlled according to fixed constraints as longas control system 120 remains in the holding mode. It may be noted,however, that some degrees of freedom of distal steerable segment 116may not require active control. For example, in orientation stiffnessmode, feedback control could actively maintain pitch and yaw of distalsteerable segment 116, while the mechanical torsional stiffness ofcatheter 110 is relied on to hold the roll angle fixed. However,catheter 110 in general may be subject to unpredictable external forcesor patient movement that would otherwise cause catheter 110 to moverelative to the work site, and active control as in process 600 isneeded to maintain or hold the desired working configuration.

Some embodiments or elements of the above invention can be implementedin a computer-readable media, e.g., a non-transient media, such as anoptical or magnetic disk, a memory card, or other solid state storagecontaining instructions that a computing device can execute to performspecific processes that are described herein. Such media may further beor be contained in a server or other device connected to a network suchas the Internet that provides for the downloading of data and executableinstructions.

Although the invention has been described with reference to particularembodiments, the description is only an example of the invention'sapplication and should not be taken as a limitation. Various adaptationsand combinations of features of the embodiments disclosed are within thescope of the invention as defined by the following claims.

What is claimed is:
 1. A medical system comprising: a cathetercontaining a mechanical system that is remotely operable to control adistal tip of the catheter; a sensor configured to at least partlymeasure a pose of the distal tip; and a control system coupled to themechanical system, wherein the control system has a plurality of modesof operation including a holding mode in which the control systemoperates the mechanical system to actively maintain a workingconfiguration of the distal tip based on feedback from the sensor. 2.The system of claim 1, wherein the plurality of operating modes of thecontrol system further includes a mode in which the control systemoperates the mechanical system to steer the catheter in response to userinput.
 3. The system of claim 1, wherein the control system and thesensor form a closed-loop system for movement and sensing of the workingconfiguration of the distal tip.
 4. The system of claim 1, wherein theworking configuration defines a position of the distal tip relative to awork site.
 5. The system of claim 1, wherein the working configurationdefines an orientation of the distal tip relative to a work site.
 6. Thesystem of claim 1, wherein maintaining the working configurationincludes maintaining a combination of a position and an orientation ofthe distal tip such that the distal tip remains pointed at a target in awork site.
 7. The system of claim 6, wherein the medical system furthercomprises a removable probe deployed in the catheter, and wherein theprobe includes a laser configured so that the working configurationpoints the laser at the target.
 8. The medical system of claim 1,wherein maintaining the working configuration comprises keeping thedistal tip on a target line.
 9. The medical system of claim 8, whereinmaintaining the working configuration further comprises maintaining anaxis of the distal tip along the target line.
 10. The system of claim 1,wherein the holding mode of the control system comprises a plurality ofsub-modes in which the control system maintains different aspects of thepose of the distal tip and wherein the control system comprises aselection module configured to place the control system in one of thesub-modes that corresponds to a type of probe deployed in the catheter.11. The system of claim 10, wherein the plurality of sub-modes includesan orientation sub-mode in which the control system maintains anorientation of the distal tip relative to a work site, and the selectionmodule places the control system in the orientation sub-mode when avision probe is deployed in the catheter.
 12. The system of claim 10,wherein the plurality of sub-modes includes a target sub-mode in whichthe control system maintains a combination of a position and anorientation of the distal tip such that the distal tip remains pointedat a target in a work site, and the selection module places the controlsystem in the target sub-mode when a probe including a laser is deployedin the catheter.
 13. The system of claim 10, wherein the plurality ofsub-modes includes an target axial sub-mode in which the control systemmaintains a combination of a position and an orientation of the distaltip such that the distal tip remains on a target line and pointed alongthe target line, and the selection module places the control system inthe target axial sub-mode when a probe including a needle is deployed inthe catheter.
 14. A control system for a catheter containing amechanical system that is remotely operable to control a distal tip ofthe catheter, and a sensor configured to at least partly measure a poseof the distal tip coupled to the mechanical system, the control systemcomprising: a plurality of modules that control operation the mechanicalsystem based on feedback from the sensor; and memory storing anindicator identifying a desired working for the distal tip, wherein eachof the modules operates the mechanical system to hold the distal tip inthe desired working configuration identified by the indicator.
 15. Thesystem of claim 14, wherein the plurality of modules includes a positionmode module that implements a process including moving the distal tipfrom a measured position to a desired position.
 16. The system of claim14, wherein the plurality of modules includes an orientation mode modulethat implements a process including moving the distal tip from ameasured orientation to a desired orientation.
 17. The system of claim14, wherein the plurality of modules includes a target mode module thatmaintains a combination of a position and an orientation of the distaltip such that the distal tip remains pointed at a target.
 18. The systemof claim 14, wherein the plurality of modules includes an target axialmode module that maintains a combination of a position and anorientation of the distal tip such that the distal tip remains on atarget line and pointed along the target line.
 19. A method comprising:steering a catheter to a working site using a mechanical system that isremotely operable to control a distal tip of the catheter; identifying aworking configuration of the distal tip, wherein the workingconfiguration poses the distal tip for performance of a medical task atthe work site; selecting one of a plurality of modes for controlling thecatheter using feedback from a sensor that measures a pose of the distaltip; and maintaining the working configuration of the distal tip throughoperation of the catheter in the selected mode.
 20. The method of claim19, wherein the plurality of modes includes a position mode thatmaintains a position of the distal tip relative to the work site. 21.The method of claim 19, wherein the plurality of modes includes anorientation mode that maintains an orientation of the distal tiprelative to the work site.
 22. The method of claim 19, wherein theplurality of modes includes a target mode that maintains a combinationof a position and an orientation of the distal tip such that the distaltip remains pointed at a target in the work site.
 23. The method ofclaim 19, wherein the plurality of modes includes an target axial modethat maintains a combination of a position and an orientation of thedistal tip such that the distal tip remains on a target line and pointedalong the target line.